1. Field
Disclosed embodiments relate to a transmission of a motorcycle.
2. Related Art
Generally, a transmission of a motorcycle includes a counter shaft to which a rotation of a crankshaft provided in an engine is transmitted through a clutch, and a drive shaft to which a rotation of the counter shaft is transmitted. When the drive shaft is rotated, the rotation thereof is transmitted to the drive shaft to thereby enable the motorcycle to run.
A plurality of drive gears are mounted on the counter shaft, and a plurality of driven gears always meshed with the drive gears are also mounted on the drive shaft.
In addition, the driven gears are rotatably mounted on the drive shaft in a gear change stage (i.e., speed shift stage) at which the drive gears are provided to be integrally rotatable with the counter shaft, and on the other hand, the driven gears are provided to be integrally rotatable with the drive shaft in a gear change state at which the drive gears are mounted on the counter shaft to be rotatable.
Further, a sliding dog gear that rotates integrally with the counter shaft or the drive shaft to be slidable is included in the drive gears and the driven gears, and the drive gears or the driven gears rotatable with respect to the counter shaft or the drive shaft are disposed adjacent to the sliding dog gear (hereinafter, these drive gears or driven gears may be referred to as “adjacent gears”).
Furthermore, a dog clutch is composed of dog pieces provided at the respective gears adjacent to the sliding dog gear, and when the gears are shifted, a gear-meshing state in a predetermined speed stage is shifted by meshing one of the dog clutches, by using a gear shift operation mechanism, so as to engage the adjacent gears with the counter shaft or the drive shaft.
However, at a time when the gears are shifted as described above, rotational speeds of the sliding dog gear and the adjacent gears are generally different from each other. Therefore, rotational speeds of the dog pieces composing the dog clutch are also different from each other, thus causing a shift shock in a case when the dog pieces with different rotational speeds are meshed with each other, thus being inconvenient.
In order to address this inconvenient matter, Japanese Patent Laid-open Publication No. 2000-205352 (Patent Document 1) discloses an arrangement in which a friction ring is disposed between the counter shaft and a fifth-speed drive gear rotatably provided on the counter shaft. By employing such a configuration, a rotation resisting force due to friction occurs between the counter shaft and the fifth drive gear at the same time when a clutch is disengaged to thereby slow down the counter shaft, thus enabling to reduce a difference of the rotational speeds between the counter shaft and the drive shaft at the time of shifting gears. According to such operation as mentioned above, it becomes possible to reduce also a difference of the rotational speeds between the sliding dog gear and the adjacent gears and a difference of the rotational speeds between the respective dog pieces, thus enabling to reduce the above-described shift shock associated with the differences of the rotational speeds.
In the conventional technology such as mentioned above, for example, when slowing down the counter shaft using the friction ring, there occurs a problem of causing a difference of rotational speeds between members between which the friction ring is interposed. Then, in view of the above matter, a difference of rotational speeds between the counter shaft and the fifth drive gear in each gear position will be described hereunder with reference to FIG. 17.
First, when driving with the fifth drive gear, a dog piece provided in a fourth drive gear, which is the sliding dog gear, is meshed a dog piece of the fifth drive gear, the counter shaft and the fifth drive gear are integrally rotated, the relative number of rotations (a difference of the number of rotations) of the counter shaft and the fifth drive gear is zero “0”, and thus there occurs no difference of the rotational speeds between the counter shaft and the fifth drive gear.
Meanwhile, when driving with the gear positions other than the fifth drive gear, the counter shaft and the fifth drive gear are not integrally rotated, and at this time, when a primary reduction ratio (gear ratio of a primary drive gear provided at the crankshaft and a primary driven gear provided at the counter shaft) is considered, the following equation is established:(number of rotations of counter shaft)=(engine rpm×primary reduction ratio)
In contrast, as for the number of rotations of the fifth drive gear, the drive shaft is slowed down with respect to the counter shaft at a reduction ratio of a selected gear position, and the fifth drive gear is driven to rotate by a fifth driven gear that rotates integrally with this drive shaft, whereby the following equation is established:(number of rotations of fifth drive gear)=(engine rpm×primary reduction ratio×reduction ratio of selected gear position×<number of fifth driven gear teeth/number of fifth drive gear teeth>)
Accordingly, since the numbers of rotations of the counter shaft and the fifth drive gear are different from each other, the relative number of rotations becomes not “0”, thereby causing the difference of the rotational speeds between the counter shaft and the fifth drive gear.
As is apparent from the above two equations, in an occasion of the engine rpm being constant, although the number of rotations of the counter shaft is constant, the number of rotations of the fifth drive gear changes according to the reduction ratio of the selected gear position. Therefore, the relative number of rotations between the counter shaft and the fifth drive gear also changes according to the reduction ratio of the selected gear position (see FIG. 17). Accordingly, there causes a problem such that when the friction ring is arranged between the counter shaft and the fifth drive gear as in the above-described conventional example, a rotation resisting force differs for every gear shift operation depending on the each selected gear position, and in such occasion, a rider cannot obtain a stable operation feeling.
Still furthermore, in the conventional arrangement, since the reduction ratio of each gear position is designed so as to increase as the gear change position becomes smaller, the relative number of rotations of the counter shaft and the fifth drive gear increases in low gear positions, such as the first drive gear and the second drive gear as compared with high gear positions, such as the fourth to sixth drive gears (see FIG. 17). Accordingly, in the arrangement in which the friction ring is arranged between the counter shaft and the fifth drive gear as in the above-described conventional example, the number of operational rotations of the friction ring in the low gear positions is increased, and in a case when a particularly large friction torque is required, an inconvenient matter will occur in durability of the friction ring.